We have, in previous studies, made a discovery that generalized transducing Salmonella phage recombine with various unrelated bacteriophages to evolve into new hybrid phage species. Recently, we isolated an unusual Salmonella typhimurium-E.coli hybrid with sensitivity to coliphage lambda and Salmonella phage P22. This bacterial strain and its derivatives have facilitated construction of new hybrid phage species between the evolutionary diverse phage lambda, which has a unique genome, and phage P22 which has a circularly permuted genome. Similarly hybrids between coli phage phi 80 and P22 phage and hybrids between coli mutator phage Mu-1 and P22 were isolated. These hybrid phages provide an excellent model for studying a mechanism of genetic evolution, control of gene expression within gene clusters derived from diverse phages, phage morphogenesis, phage chromosome structure, antigen conversion and nature of transduction. To understand the above mechanisms, we propose to study the following: (1) Regulation of the Mu-1 late genes by the P22 early genes in Mu-P22 phage replication; (2) Fine genetic mapping of the homology betwen Mu-P22 hybrid and its parental phages Mu-1 and P22; (3) Isolation of P22-Mu hybrids carrying the P22 protein coat and some Mu-1 early genes; (4) Isolation of P22-Mu hybrids carrying the mutator function expressed in S. typhimurium; (5) Isolation of P22-phi 80 hybrid phages; (6) Characterization of the transducing capacities of various hybrid phages; phi 80-P22, P22-phi 80, Mu-P22 and P22-MU; and (7) Salmonella 0-1 antigen conversion in other bacterial species by some lambda-P22 hybrids carrying the antigen conversion gene al. BIBLIOGRAPHIC REFERENCES: Sato, M., Yamada, T., Yamamoto, K. and Yamamoto, N. (1976) Evidence for hybrid formation between rubella virus and a latent virus of BHK21/Wi-2 cells. Virology 69, 691-699. Baron, L.S., Life, C.A., Gemski, P. and Yamamoto, N. Expression of Salmonella Somatic Antigen 0-1 in Escherichia coli K-12. Abt. Am. Soc. Microbial., 1977, in press.